1. Field of the Invention
The present invention relates to an impact test apparatus and an impact test method that can obtain an impact stress-strain characteristic of a test piece.
2. Description of Related Art
An Izod impact test or a Charpy impact test has been conventionally known as a method of measuring the impact strength of a material (for example, see Japanese Unexamined Patent Publication No. H2(1990)-13825). According to these methods, when an impact energy (impact force) is applied to a test piece to break a test piece, the impact strength of the test piece can be measured from the impact energy. However, in the case of a test piece formed of an impact absorbing material of a foaming material, a viscoelastic material, or a combination of these materials, when the impact force is applied to the test piece, the test piece is elastically deformed to absorb the impact energy (impact force). Hence, it is difficult to evaluate an impact force applied to the test piece and an impact stress-strain characteristic of the test piece when the impact force is applied to the test piece. For this reason, in the impact absorbing material, the characteristic of the impact absorbing material has been evaluated by measuring an impact absorbing property or an repulsion property that are found by a Lubke impact resilience test method or a Trypso impact resilience test method (see, for example, Japanese Standards Association JIS Handbook Rubber (issued on Apr. 1, 1999).
By the way, a foaming material, a viscoelastic material, or a combination of these materials has been used as the impact absorbing material of various kinds of machines and electric appliances. Portable machines and electric appliances (for example, cellular mobile phone) have been increased in number in recent years. In these various products, an impact force is applied to them in a manner that has never been hitherto conceivable.
Moreover, these impact absorbing materials have different impact absorbing properties according to material, internal form, or the like. Hence, it becomes difficult to evaluate the impact absorbing materials by the conventional impact tests or repulsion elasticity test on the same basis. Therefore, these impact absorbing materials are placed on actual products and impact drop tests or the like are conducted on the actual products. In this manner, a durability evaluation test or the like for impact is conducted on the product.